Downregulation of FGF Signaling by Spry4 Overexpression Leads to Shape Impairment, Enamel Irregularities, and Delayed Signaling Center Formation in the Mouse Molar.

FGF signaling plays a critical role in tooth development, and mutations in modulators of this pathway produce a number of striking phenotypes. However, many aspects of the role of the FGF pathway in regulating the morphological features and the mineral quality of the dentition remain unknown. Here, we used transgenic mice overexpressing the FGF negative feedback regulator Sprouty4 under the epithelial keratin 14 promoter (K14-Spry4) to achieve downregulation of signaling in the epithelium. This led to highly penetrant defects affecting both cusp morphology and the enamel layer. We characterized the phenotype of erupted molars, identified a developmental delay in K14-Spry4 transgenic embryos, and linked this with changes in the tooth developmental sequence. These data further delineate the role of FGF signaling in the development of the dentition and implicate the pathway in the regulation of tooth mineralization. © 2019 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research

FGF Signaling Regulates the Number of Posterior Taste Papillae by Controlling Progenitor Field Size

The sense of taste is fundamental to our ability to ingest nutritious substances and to detect and avoid potentially toxic ones. Sensory taste buds are housed in papillae that develop from epithelial placodes. Three distinct types of gustatory papillae reside on the rodent tongue: small fungiform papillae are found in the anterior tongue, whereas the posterior tongue contains the larger foliate papillae and a single midline circumvallate papilla (CVP). Despite the great variation in the number of CVPs in mammals, its importance in taste function, and its status as the largest of the taste papillae, very little is known about the development of this structure. Here, we report that a balance between Sprouty (Spry) genes and Fgf10, which respectively antagonize and activate receptor tyrosine kinase (RTK) signaling, regulates the number of CVPs. Deletion of Spry2 alone resulted in duplication of the CVP as a result of an increase in the size of the placode progenitor field, and Spry1−/−;Spry2−/− embryos had multiple CVPs, demonstrating the redundancy of Sprouty genes in regulating the progenitor field size. By contrast, deletion of Fgf10 led to absence of the CVP, identifying FGF10 as the first inductive, mesenchyme-derived factor for taste papillae. Our results provide the first demonstration of the role of epithelial-mesenchymal FGF signaling in taste papilla development, indicate that regulation of the progenitor field size by FGF signaling is a critical determinant of papilla number, and suggest that the great variation in CVP number among mammalian species may be linked to levels of signaling by the FGF pathway

Expression of MicroRNAs in the Stem Cell Niche of the Adult Mouse Incisor

Peer reviewe

Identification and characterization of AJ18, a novel zinc finger transcription factor expressed during skeletal development

grantor: University of TorontoIn response to osteo-inductive signals generated by the bone morphogenetic proteins (BMPs), undifferentiated mesenchymal stem cells can differentiate into osteoblasts. However, the molecular mechanisms that coordinate and direct osteogenesis are largely unknown. Differential display was utilized to identify a gene, provisionally named 'AJ18', whose expression is responsive to BMP-7 and up-regulated during osteoblastic differentiation in fetal rat calvarial cells (FRCCs). 'AJ18' encodes a novel protein comprising a Krûppel-associated box (KRAB) domain, which is a well-characterized transcription repressor motif, and 11 successive C2H2 zinc finger motifs. Using a target detection assay, a consensus DNA-binding site with the sequence 5'-CCACA-3' was revealed. This sequence is present in the enhancer for 'Runx2' (OSE2, osteoblast-specific element 2; 5'-ACCACA-3 '), a master gene for osteogenesis. By using a transient transfection assay AJ18 expression was found to abrogate the transactivation activity of Runx2 in a dose-dependent manner. To study the regulation of 'AJ18' gene expression, a rat genomic library was screened to obtain the 5'-flanking region of 'AJ18'. Mapping of the transcription start site showed that the 'AJ18' gene contains an unusually long 2.3 kb 5 '-untranslated region (5'-UTR) with potential for strong secondary structure. Chimeric constructs encompassing the immediate promoter region (77 to +177) revealed strong transcriptional activity when ligated to a luciferase reporter gene in transient transfection assays. Addition of ~2 kb of upstream sequence did not increase this activity. Comparison of mouse and rat 'AJ18' promoters however revealed high sequence identity that included several responsive elements for proteins such as Runx2, NF[kappa]B, Smads, Sp1, and Ets1. The expression of AJ18 mRNA and protein at various stages of mouse development revealed high levels in brain, kidney, and mineralized tissues during embryonic development. In developing endochondral bone, AJ18 staining was strong in proliferating and pre-hypertrophic chondrocytes, and osteoblasts, with low or no staining in hypertrophic chondrocytes. Nuclear staining was also observed in differentiating cells that form the mineralized tissues of teeth. Notably, the expression of AJ18 was similar to the expression of BMP-7 consistent with its perceived role as a transcriptional factor that regulates developmental processes downstream of BMP-7. These studies, therefore, have identified the first KRAB/C2H 2 zinc finger gene to be implicated in skeletal development, and have characterized the first promoter sequence for a gene belonging to the large KRAB/C2H2 zinc finger family.Ph.D

Neural crest-mediated bone resorption is a determinant of species-specific jaw length

© 2015 The AuthorsPrecise control of jaw length during development is crucial for proper form and function. Previously we have shown that in birds, neural crest mesenchyme (NCM) confers species-specific size and shape to the beak by regulating molecular a

Spontaneous emergence of overgrown molar teeth in a colony of Prairie voles (Microtus ochrogaster)

© 2015 WCSS.Continuously growing incisors are common to all rodents, which include the Microtus genus of voles. However, unlike many rodents, voles also possess continuously growing molars. Here, we report spontaneous molar defects in a population of Prai

IGF-1 TMJ injections enhance mandibular growth and bone quality in juvenile rats

ObjectivesDentofacial orthopaedic treatment of mandibular hypoplasia has unpredictable skeletal outcomes. Although several biomodulators including insulin-like growth factor 1 (IGF-1) are known to contribute to chondrocyte proliferation, their efficacy in modulating mandibular growth has not been validated. The aim of this study was to determine the effect of locally delivered IGF-1 on mandibular growth and condylar bone quality/quantity in juvenile rats.Setting and sample populationInstitutional vivarium using twenty-four 35-day-old male Sprague-Dawley rats.MethodsPBS or 40��g/kg (low-dose) IGF-1 or 80��g/kg (high-dose) IGF-1 was injected bilaterally into the temporomandibular joints of the rats at weekly intervals for four weeks. Cephalometric and micro-computed tomography measurements were used to determine mandibular dimensions. Bone and tissue mineral density, volume fraction and mineral content were determined, and serum IGF-1 concentrations assayed.ResultsIntra-articular administration of high-dose IGF-1 contributed to a significant 6%-12% increase in mandibular body and condylar length compared to control and low-dose IGF-1-treated animals. Additionally, IGF-1 treatment resulted in a significant decrease in the angulation of the lower incisors to mandibular plane. Condylar bone volume, bone volume fraction, mineral content and mineral density were significantly increased with high-dose IGF-1 relative to control and low-dose IGF-1 groups. Serum IGF-1 levels were similar between all groups confirming limited systemic exposure to the locally administered IGF-1.ConclusionLocal administration of high-dose 80��g/kg IGF-1 enhances mandibular growth and condylar bone quality and quantity in growing rats. The findings have implications for modulating mandibular growth and potentially enhancing condylar bone health and integrity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172354/1/ocr12524.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172354/2/ocr12524_am.pd